Extendable fins on ammunition facilitate firing, at the same time increasing the stability of the shell in its ballistic trajectory, and therefore the range and probability of hitting.
Extendable fins are previously well known. Thus, for example, a narrow groove in a main fin or the body of the unit, is arranged a spring fin which is supported at its front end, and which when spread springs forth with its rear parts above the main fin or the envelope surface of the unit so that it inclines obliquely outwards and rearwards.